Chrome headless update : Adapt to new headless or use chrome headless-shell ?

[cderv]

Following up on #329 and what will be done in chromote

• https://github.com/rstudio/chromote/issues/171

[cderv]

Old headless mode was removed: developer.chrome.com/blog/removing-headless-old-from-chrome

This means there may be nothing to do with pagedown anymore. --headless is used and will continue to work, while using new mode.

Possibly, using the new chome-headless-shell could be used with pagedown instead. https://developer.chrome.com/blog/chrome-headless-shell